ZXSC100 Zetex Semiconductors plc., ZXSC100 Datasheet - Page 14

• Manufacturer Part Number: ZXSC100
• Description: Single Cell Dc-dc Converter Solution
• Manufacturer: Zetex Semiconductors plc.

Designing with the ZXSC100
Introduction
This section refers to the ZXSC100, 3.3V/100mA
output reference design and demonstrates the
dynamic performance of the solution.
Figure 1.
ZXSC100 low power solution, 3.3V/100mA output.
Efficiency
Efficiency is often quoted as one of the key parameters
of a DC-DC converter. Not only does it give an
instantaneous idea of heat dissipation, but also an
idea as to the extent battery life can be extended.
Figure 2. Shows the efficiency of the ZXSC100 low
power solution. Efficiency v Output current is shown
for a 3.3V output at various input voltages.
V
Figure 2.
ZXSC100 efficiency v output current
ZXSC100
BATT
V
BATT
S E M I C O N D U C T O R S
C1
220µF
C1
220µF
R1
0R
U1
ZXSC100
R1
0R
EM
BAS
RE
V
CC
U1
ZXSC100
EM
BAS
RE
V
L1
22µH
CC
V
I
SENSE
DRIVE
L1
22µH
G
FB
ND
V
I
SENSE
DRIVE
G
FB
ND
Q1
FMMT617
ZHCS1000
R2
0.033R
Q1
FMMT617
R2
0.033R
ZHCS1000
D1
D1
R3
110K
R4
30K
R3
110K
R4
30K
C3
1NF
3.3V/0.1A
C3
1NF
3.3V/0.1A
C2
220µF
C2
220µF
14
Figure 4.
I
Main switching waveforms
Steady state operation under constant load gives an
excellent indication of ZXSC100 performance.
Represented in Figure 3. is the main switching
waveform, measured at the collector of Q1, indicating
the transistor on-state and the diode energy transfer to
the output.
Figure 3.
Switching waveform
The peak switching current is derived from the
threshold of the I
(see Applications section for calculations). Figure 4.
shows the switching waveform associated with the
I
SENSE
SENSE
threshold
pin
SENSE
pin and the sense resistor value
ISSUE 3 - JANUARY 2004